It is already described in EP 1 009 003 B1 to provide an arrangement with a control device comprising an electromagnet, the arrangement comprising at least one holding coil positioned in series with an electronic switch, connected to the terminals of a supply voltage of the coil, measuring means for measuring the holding current flowing in the holding coil, control means for actuating the electromagnet as well as means for supplying power to the control means. The means for supplying power to the control means are connected in series with the holding coil and the electronic switch so that they are supplied with holding current. The holding current measuring means comprise a measuring switch which is connected in parallel with the power supply means of the control means and has an additional electronic switch, and also comprise a measuring resistor connected in series therewith. The control means are connected to the terminals of the resistor and to a control electrode of the additional electronic switch, the additional electronic switch being switched into the conducting state at regular intervals. The power supply means comprise a Zener diode, connected in series with the coil and the electronic switch, and a further diode which is connected in series with a capacitor to the terminals of the Zener diode. The power supply means further comprise a diode connected in series with the Zener diode or a voltage regulation circuit connected in parallel with the capacitor. An auxiliary voltage supply regulation circuit is connected in parallel with a capacitor. The auxiliary supply voltage is supplied to a microprocessor. A second auxiliary supply voltage which is not regulated is the voltage for this capacitor. The passage of a regulated holding current through the coil is controlled by the microprocessor. At periodic intervals, the microprocessor acts simultaneously on two of the outputs thereof which each lead to a transistor, these transistors being connected to the supply circuit on the source side in one case and on the gate side in the other. The microprocessor sends control commands to the two transistors during the time required to measure the voltage at the resistor which is connected on the source side to one of the two transistors. The other transistor is connected on the gate side to a voltage adjustment circuit which in turn is positioned at one of the signal outputs of the microprocessor.
DE 299 09 901 U1 proposes an electronic drive control means for a contactor drive containing a drive coil and an armature. In order to provide drive control without controlling the coil current, an average actuation current of optimal size is produced by means of a respective pulse width of the drive coil within a wide static and dynamic range of a supply voltage with high dynamics provided by a rectifier circuit. This is achieved both during the pull-in and holding procedures. High dynamics are achieved from the pulse width control derived from the supply voltage alone by avoiding coil current measurement. The average actuation voltage should be virtually independent of the supply voltage and assume such a value that the armature is attracted with optimal closing dynamics and is held securely with minimal power. A microprocessor monitors the input voltage to ensure that it remains within a permissible voltage range and when it falls below or exceeds this range the contactor drive is prevented from switching on or, when this range is reached, the contactor drive is activated.
In EP 1 009 003 B1, the clocked transistor is connected or disconnected as a function of the current measured. Increased circuit complexity is therefore required to regulate the pull-in or holding current owing to the measuring resistor.
A pulse-width modulation operation is described in DE 10 2007 031 995.